Multicast, or one-to-many, communications are important for supporting emerging distributed applications. In photonic space-switched networks, multicast communications can be easily and cost-effectively implemented with optical splitters. However, in multi-wavelength photonic networks, multicast switching requires wavelength converters to allow a channel at a distinct optical frequency to be broadcast to other channels at other distinct optical frequencies. Such photonic wavelength converters are expensive, and thus it is preferable to minimize the number of photonic converters in a network.
To date, there has been little work performed on photonic multicast switches having wavelength conversion capabilities. However, there are currently many candidate architectures for unicast multi-wavelength switches having wavelength conversion capabilities. Two of these architectures are easily generalized into designs for multicast switches having wavelength conversion capabilities: 1.) a non-blocking architecture based on dedicated frequency converters; and 2.) a blocking architecture based on shared frequency converters. Each of these architectures, and their shortcomings with respect to their use in multicast communications, are discussed briefly below.
An optical cross-connect with dedicated wavelength converters may be implemented by extending the architecture proposed in B. Ramamurthy et al., “Wavelength-conversion in WDM networking,” IEEE Journal on Selected Areas on Communications, vol. 16, pages 1061–1073, September 1998, which is hereby incorporated by reference herein in its entirety. In such an optical cross-connect, all-optical wavelength converters are dedicated to individual channels at inputs or outputs of an optical space switch fabric. When the space switch fabric is unicast and non-blocking, the overall cross-connect becomes a unicast strictly non-blocking wavelength-interchanging cross-connect. When the space switch fabric is multicast and non-blocking, the overall cross-connect becomes a multicast strictly non-blocking wavelength-interchanging cross-connect.
The above-described cross-connect has many advantages, including its simplicity and the absence of cascaded frequency conversions. However, it suffers from large converter requirements of O(F.W), wherein F represents the required number of fibers and W represents the number of wavelengths per fiber.
An optical cross-connect with shared wavelength converters may also be implemented by extending the architecture proposed in B. Ramamurthy et al., “Wavelength-conversion in WDM networking,” IEEE Journal on Selected Areas on Communications, vol. 16, pages 1061–1073, September 1998, which was previously incorporated by reference herein in its entirety. In such an optical cross-connect, a small number of all-optical wavelength converters are shared at inputs or outputs of an optical space switch fabric. Beneficially, the total number of wavelength converters may be strictly smaller than the total number of wavelength channels. However, the resulting multicast cross-connect is blocking and may not be appropriate in situations where a high level of network utilization is expected.
In view of the foregoing, it would be desirable to provide a technique for multicasting an optical frequency channel in a multi-channel optical system which overcomes the above-described inadequacies and shortcomings in an efficient and cost effective manner.